Due primarily to desorption techniques, mass spectrometry has been quite successful in analyzing a variety of biomolecules. Specifically, peptides arising from tissue extracts or from chemical synthesis can be directly analyzed without prior derivatization. Modification of the peptide structure may be due to changes occurring during chemical synthesis or due to post-translational processing occurring during biosynthesis. Both types of modifications can alter the biological activity of the particular peptide. Identification of these structural changes is necessary for a thorough understanding of the peptide's activity. Generation of structural and functional diversity as a consequence of modification has continued to be our interest. A variety of investigators have availed themselves of our knowledge and experience in analyzing chemically-synthesized peptides. In most instances, peptide lots display divergent biological activities. The structural basis for these divergent activities is sought and usually found to be some type of synthetic byproduct or impurity. Chemical derivatives, proteins, and polysaccharides have also been analyzed in the laboratory in support of other laboratory research.